A minimal fix for the regression introduced in the previous commit

The refactoring in that commit was performed incorrectly, such that
it would no longer detect as invalid an incomplete series of
continuation bytes at the end of a string.
Improve on previous fix

This version tries to force the real decoding function to be inlined
into each of its callers, which in turn each have different criteria
for backing up a byte. This avoids an extra test at the end of
strict decoding.

While this seems to fix gh-61, I want to beef up the test suite so
that it will correctly detect the bug.
Ensure that t_utf8_err gets fed *only* invalid UTF-8 inputs

This test currently fails due to gh-61.

--HG--
extra : amend_source : ca66a1e6503a0cb9cf6cf5f2b82f2199133a6512
Merge
Merge fix for gh-61 into 1.0 branch
Bump version to 1.0.0.1
Amend release notes
Merge from 1.0 branch